MongoDB - $push accumulator is slowing query down - mongodb

Question

To develop a web application, I use MongooDB as Back-End and I need to retrieve data from it. On a particular page I need to recover prices' history from specific brands. In my MongoDB collection, here is how a document/product is saved :
{
brand : "exampleBrand"
prices : Array
0: Object
date "2022-03-08"
price: 1900
1: Object
date "2022-03-09"
price: 1910
}
My goal is then to retieve dates and prices from a specific brand in the following format :
{
{
date : "2022-03-08",
prices : [price_product1, priceproduct2,...]
}
{
date : "2022-03-09",
prices : [price_product1, priceproduct3,...]
}
}
In order to do that I have designed the following query :
db.Prices.aggregate([
{
$match: {
{brand: "exampleBrand"}],
},
},
{
$project: {
_id: 0,
prices: 1,
},
},
{
$unwind: '$prices',
},
{
$group: {
_id: "$prices.date",
prix: {
$push: "$prices.price",
},
},
},
]);
Once I have these results I can go on with different calculations etc... to display on my page. However, there are approcimatively 90000 documents, each of them having in average 30 prices and dates. Thus, the group stage of the aggregation pipeline is taking a long time.
I have try different indexes on "prices", "prices.date", "brand, prices" but none of them seem to speed up the query. I have also tried twisting and changing the query but couldn't find a more efficient way to get my results. Would anyone have an idea on how to achieve this ?
Thank you,

Answer 1

For faster querying here with these conditions I think the only way is to use mechanisms like Redis or Memcached because the query, especially in the array, would cost a lot of io and process for the aggregation process.
P.S. I doubt that but if you somehow are able to change your data structure in a way that it would be flat it would be faster but not like caching method faster.
example:
{
brand : "exampleBrand"
price1 : 1900
date1 : "2022-03-08"
price2 : 2100
date2 : "2022-03-29"
}